The grey forecasting model, GM(1,1) was adopted in this study to capture the development trends of the number of motor vehicles, vehicular energy consumption and CO2 emissions in Taiwan during 2007-2025. In addition, the simulation of different economic development scenarios were explored by modifying the value of the development coefficient, a, in the grey forecasting model to reflect the influence of economic growth and to be a helpful reference for realizing traffic CO2 reduction potential and setting CO2 mitigation strategies for Taiwan. Results showed that the vehicle fleet, energy demand and CO2 emitted by the road transportation system continued to rise at the annual growth rates of 3.64%, 3.25% and 3.23% over the next 18 years. Besides, the simulation of different economic development scenarios revealed that the lower and upper bound values of allowable vehicles in 2025 are 30.2 and 36.3 million vehicles, respectively, with the traffic fuel consumption lies between 25.8 million kiloliters to 31.0 million kiloliters. The corresponding emission of CO2 will be between 61.1 and 73.4 million metric tons in the low- and high-scenario profiles. (C) 2009 Elsevier Ltd. All rights reserved.